Ribbons of fibers are the natural way to handle a large number of fibers. (The number can vary from a few to a few dozens). Ribbons are commonly used in fiber communication since the fibers are densely connected and there are standard connectors that can be coupled to them. The use of ribbons is the natural solution for back plane connectors, where high density connectivity and a large number of fibers are required. Usually bundles are made from single fibers and then assembled (at least at one end) in ribbons to fit the standard connectors
With the growing demand for bandwidth, the active optical components, such as optical sources and photo-receivers, were produced and used in the form of matrices of N×M elements. This is particularly true for VCSEL matrices and matrices of photodiodes. In other words, arrays of optical fibers must be coupled precisely and reliably to semiconductor lasers and detector arrays on a chip. In this context, there is a great demand for optical fiber bundles in general and for bundles made from ribbons, in particular, as well as for a reliable and efficient method of producing such bundles.
In U.S. Pat. No. 6,704,483 to Sherman, a method for creating an accurate fiber array from individual optical fibers is described. The method includes removing the fiber jackets and buffer layers of each fiber and shaping the stripped fiber tips to a conical shape. A special tool to hold the fibers is required. The conical tips are inserted through a guide plate until they reach the end and can be inserted through mask holes where they are affixed in silicon or epoxy. This method requires extreme precision of hole centers in the silicon wafer—typically a tenth of a micron for 120-200 micron holes.
This method is not suitable when using a fiber ribbon since all the fibers in a ribbon are connected together, so that stripping and making a conic end for each of them separately would require the ribbon to be disassembled, thereby taking away all the advantages of ribbons. Furthermore, while a few fibers can be inserted simultaneously, this solution requires a series of guide plates inside the housing. This would not work with ribbons, which have low precision for each fiber in their jackets and even stripped. This means, when putting such ribbon fibers in holes, some of the fibers would be stopped/stacked in the hole before the end, while the rest of the fibers would be floating, not reaching the end of the plate, and thus will not get the accuracy needed for assembly.
U.S. Pat. No. 6,766,086, also to Sherman, describes a method of engagement of individual fibers used to achieve precise placement in a fiber array housing. This involves at least one movable arm or clamp attached to the mask on the housing for pressing the fiber against the side walls of the fiber seating openings in the mask.
U.S. Pat. No. 6,757,475, also to Sherman, describes a method of making an etchable wafer substrate for use in making optical fiber array plates including forming a series of metrology holes at one or more locations of the wafer. When the wafer is preliminarily completed, the variation between designed plate hole diameter and the actual plate hole diameter is determined, by using a probe known to be of the desired diameter. Corrective action can be taken before the wafer ships, e.g., the size of the various holes can then be adjusted accordingly, thereby permitting manufacturers to know the precise hole size without the use of optical instruments.
Accordingly, there is a long felt need for a method for creating a bundle of fiber ribbons, and it would be very desirable if there were precise positioning of each of the fibers from each ribbon.